1. Field of the Invention
This invention relates to adhesives used in the spraying of insulating fibers.
2. Description of the Prior Art
In the art of spraying fibers with adhesives onto a surface such as a wall or ceiling, it is desirable to produce a product which is flame retardant; fast drying and quick setting; strong; flexible; resistant to mildew, corrosion, and condensation; able to be applied in desired thicknesses and to a variety of substrates; and having desired color characteristics. No prior art process, method, device, or composition teaches or suggests a product with these characteristics.
In spraying fibers, the spray itself is made up of two primary components--the fibers and an adhesive. Adhesives are generally water-based. The adhesive/water mixture keeps the fibers in place in a manner similar to the way in which saliva maintains the integrity of a "spit ball" until the adhesive sets. A typical prior art adhesive is Sodium Silicate such as Grade 40 or 42. This adhesive has proven to be unacceptable. The product resulting from a spray using this Sodium Silicate as an adhesive is brittle and non-flexible and does not withstand the expansion and contraction of the substrate to which the spray is applied. This product lacks cohesive strength and falls out in flakes and chunks. Also this product has an undesirable yellow color and is especially undesirable when utilized in exposed interior applications.
Other prior art adhesives are acrylics, vinyl acrylic, and polyvinyl acetates. These are all used as water-based adhesives. Such adhesives are not fire-resistant or flame-retardant. On the contrary, they are highly combustible and contribute to rather than inhibit a fire. One solution to the problems associated with the fire-enhancing characteristics of these adhesives was to overspray the final product with a material such as Sodium Silicate or Anhydrous Boric Acid in a water solution.
With an acrylic adhesive the maximum thickness which could be sprayed onto a celing for one setting was approximately two and a half inches; but at this and at lesser thicknesses there were often areas of fallout or "patties." The strong interlocking and adhesion of the fibers would not occur until the product dried to a moisture content of about 15%. At this low moisture content acrylics would be inhibited from returning into solution and would not set properly. Prior to reaching the 15% moisture content level, the acrylics could be washed out of the product by water from condensation or water leaks. One attempt to maintain the acrylics in the product involved the addition of aluminum sulfate to the fibers. This made the acrylics coalesce into a stringy film and prevented the acrylic film from migrating through the fibers. The resultant product was unacceptable because of thickness limitation and because acrylics are combustible.
A product utilizing an acrylic as an adhesive exhibited the following flame and smoke characteristics:
______________________________________ Flame Spread 20 Fuel Contributed 10 Smoke Developed 0 ______________________________________
where untreated red oak has a rating of 100 for all three categories and where asbestos cement board has a rating of 0 for all three categories.
Other prior art adhesives include acrylic emulsion, polyvinyl chloride, polyvinyl acetate, acrylic esters, and vinylidene chloride copolymer, all of which exhibit some or all of the problems and limitations already discussed.